Biomedical subjects

J D Featherstone

Publications and source records attributed to J D Featherstone.

At least 19 recordsLinked to original sources

PubMed2001

Effect of CO2 laser on pulpal temperature and surface morphology: an in vitro study.

OBJECTIVES: The objective of this study was to evaluate the potential effects on underlying dental hard tissues of a high pulse rate carbon dioxide (CO2) laser that was designed for soft tissue surgery. METHODS: Eighteen extracted human teeth were sectioned longitudinally, cleaned, and varnished, leaving nine exposed windows on each: six on the coronal surface (enamel) and three on the root surface (cementum, dentin). The CO2 irradiation conditions used were: wave length 10.6 microm; 1.2-2.6J/cm(2) fluence per pulse; repetition rate 120-1000Hz; 100-200ms pulse duration; and cumulative fluences ranging from 14 to 2200J/cm(2). Each window was irradiated with a 0.3mm beam diameter at one of nine power settings for 0.1, 0.5, or 1.0s. The pulp chamber temperature was measured with a microthermocouple. The irradiated teeth were evaluated by Polarized Light Microscopy (PLM) and Scanning Electron Microscopy (SEM). RESULTS: The pulp chamber temperature rise ranged from 0.5 to 19 degrees C depending on the location of the window and distance to pulp chamber. SEM revealed crystal fusion in both enamel and dentin at all cumulative fluences. At cumulative fluences of 40J/cm(2), 200 pulses/second and higher, measurable tissue loss was observed with PLM both in dentin and enamel. CONCLUSIONS: These results indicate there are threshold conditions above which pulsed CO2 laser light used for soft tissue surgery may cause detrimental changes to underlying oral hard tissue and to the pulp.

Body Temperature↗

PubMed2001

Dental hard tissue modification and removal using sealed transverse excited atmospheric-pressure lasers operating at lambda=9.6 and 10.6 microm.

Pulsed CO(2) lasers have been shown to be effective for both removal and modification of dental hard tissue for the treatment of dental caries. In this study, sealed transverse excited atmospheric pressure (TEA) laser systems optimally tuned to the highly absorbed 9.6 microm wavelength were investigated for application on dental hard tissue. Conventional TEA lasers produce an initial high energy spike at the beginning of the laser pulse of submicrosecond duration followed by a long tail of about 1-4 micros. The pulse duration is well matched to the 1-2 micros thermal relaxation time of the deposited laser energy at 9.6 microm and effectively heats the enamel to the temperatures required for surface modification at absorbed fluences of less than 0.5 J/cm(2). Thus, the heat deposition in the tooth and the corresponding risk of pulpal necrosis from excessive heat accumulation is minimized. At higher fluences, the high peak power of the laser pulse rapidly initiates a plasma that markedly reduces the ablation rate and efficiency, severely limiting applicability for hard tissue ablation. By lengthening the laser pulse to reduce the energy distributed in the initial high energy spike, the plasma threshold can be raised sufficiently to increase the ablation rate by an order of magnitude. This results in a practical and efficient CO(2) laser system for caries ablation and surface modification.

Dental Caries↗

PubMed2001

Anticaries profile qualification of an improved whitening dentifrice.

A series of pH cycling "profile" laboratory studies was conducted to confirm the anticaries potential of an enhanced cleaning and whitening dentifrice based on a novel abrasive polishing silica and pyrophosphate tartar control source, with sodium fluoride as the anticaries ingredient. Under pH cycling remineralization conditions, the whitening dentifrice produced lesion fluoridation comparable to a conventional tartar control dentifrice containing combinations of pyrophosphate anion and a NaF fluoride ion source. Under pH cycling lesion progression conditions, the whitening dentifrice produced enamel protection against caries development, comparable to control dentifrices containing NaF alone or in combination with tartar control pyrophosphate anion. These results are consistent with clinical data supporting the effectiveness of NaF dentifrices combined with anionic tartar control inhibitors such as pyrophosphate. These results support the anticaries effectiveness of the enhanced cleaning and whitening dentifrice based upon "Stain-Specific Soft Silica."

Analysis of Variance↗

PubMed2000

Studies of dental root surface caries. 1: Comparison of natural and artificial root caries lesions.

Qualitative polarized light microscopy and cross-sectional microhardness testing profiles were used to compare artificial root caries lesions with those naturally present in extracted human teeth. The artificial lesions were produced by immersion of roots with exposed windows in chemical buffers of acetate and lactate with no added enzymes or bacteria. The three buffer systems used produced lesions with the range of histological characteristics of natural lesions. These included a 'body' or 'surface' zone of the lesion when viewed in water, and a 'frontal' zone of reverse birefringence when viewed in quinoline. The 'frontal' zone was noted to first develop after three days of immersion in acetate buffer. Advanced natural lesions exhibited a wide, diffuse, advancing front, which was similar to that produced by 28-60 day lesions in acetate. Microhardness profiles of natural lesions could all be matched by one or more of the artificial lesions. The demineralizing process was seen to reduce mineral content across the lesion from 45 per cent in normal dentine to between 15 and 25 per cent.

Acetic Acid↗

PubMed2000

Studies of dental root surface caries. 2: The role of cementum in root surface caries.

Artificial caries lesions were produced in roots of teeth using an acetate buffer system, when the layer of cementum was either normal in thickness, excessively thickened by hypercementosis, or had been removed completely. The rates of lesion progression were measured in each case using polarized light microscopy to measure lesion depth. Analysis of calcium (Ca) and phosphorus (P) loss during the demineralizing process was carried out. The removal of cementum was found to significantly increase the initial rate of penetration of the lesion into the root, although this rate progressively reduced to a level consistent with that found in normal roots after seven days of demineralization. The overall depth remained consistently greater than that observed in normal roots, or when lesions were produced entirely within hyperplastic cementum. Chemical analysis also showed removal of cementum resulted in an initial doubling of the Ca and P lost from the root surface. Prior direct exposure of segments of normal roots to the oral environment was found not to significantly alter the rate of artificial lesion progression, in comparison with that in the originally protected segment of the root surface. It was concluded that an intact cementum layer has the intrinsic ability to protect the underlying dentine of exposed tooth roots against acidic demineralization and that prior exposure to the oral environment does not significantly alter this ability.

Calcium↗

PubMed2000

The science and practice of caries prevention.

BACKGROUND AND OVERVIEW: Dental caries is a bacterially based disease. When it progresses, acid produced by bacterial action on dietary fermentable carbohydrates diffuses into the tooth and dissolves the carbonated hydroxyapatite mineral--a process called demineralization. Pathological factors including acidogenic bacteria (mutans streptococci and lactobacilli), salivary dysfunction, and dietary carbohydrates are related to caries progression. Protective factors--which include salivary calcium, phosphate and proteins, salivary flow, fluoride in saliva, and antibacterial components or agents--can balance, prevent or reverse dental caries. CONCLUSIONS: Caries progression or reversal is determined by the balance between protective and pathological factors. Fluoride, the key agent in battling caries, works primarily via topical mechanisms: inhibition of demineralization, enhancement of remineralization and inhibition of bacterial enzymes. CLINICAL IMPLICATIONS: Fluoride in drinking water and in fluoride-containing products reduces caries via these topical mechanisms. Antibacterial therapy must be used to combat a high bacterial challenge. For practical caries management and prevention or reversal of dental caries, the sum of the preventive factors must outweigh the pathological factors.

Adolescent↗

PubMed2000

Caries detection and prevention with laser energy.

Laser light can be used in the visible region (blue or red) as a tool for the detection of carious lesions. Techniques developed to date for early caries detection by laser light rely on fluorescence naturally from the tooth material or from bacterial by-products. Fluorescence techniques have been introduced clinically in Europe and show great promise for improved management of dental caries. Laboratory studies have shown that specific laser irradiation that is absorbed strongly by the carbonated hydroxyapatite mineral of the teeth can heat a thin layer at the surface briefly, altering its composition and making it strongly resistant to subsequent acid attack in the caries process. This resistance leads to major inhibition of subsequent subsurface caries progression and shows great promise for the treatment of susceptible sites on the tooth. This technology, if used in conjunction with ablation of carious lesions by specific laser irradiation, could prevent secondary progression around restorations.

Carbon Dioxide↗

PubMed1999

Characterization of the mechanical and ultrastructural properties of heat-treated cortical bone for use as a bone substitute.

Heat-treated bovine cortical bone has been proposed as an alternative to bone grafts and synthetic bone substitutes because it may combine the advantages of allografts (high stiffness and strength) and synthetic materials (abundant supply, reduced risk of rejection and disease transfer). Its mechanical properties and ultrastructure, however, are not well characterized. To address this, we compared the compressive (n = 20, bovine bone) and tensile (n = 26, bovine bone) mechanical properties and the ultrastructure (n = 12, human bone) of intact versus 350 degrees C heat-treated cortical bone. The 350 degrees C heat-treated bone had a mean +/- SD elastic modulus similar to the intact bone for both compression (16.3 +/- 2.2 GPa, pooled; p = 0.68) and tension (16.3 +/- 3.7 GPa, pooled; p = 0.95). It also maintained 63% of the intact strength in compression but only 9% in tension (p < 0.001). Infrared scans and X-ray diffraction patterns showed no differences between the 350 degrees C heat-treated and intact bone but large differences between ashed (700 degrees C) and intact bone. Similarly, heat-treated bone previously has been shown to be biocompatible and osteoconductive. We conclude, therefore, that 350 degrees C heat-treated cortical bone may be an excellent load-bearing bone substitute provided that it is loaded in compression only in vivo and is shown by future work to have acceptable fatigue properties.

Aged↗

PubMed1999

Modeling the modification depth of carbon dioxide laser-treated dental enamel.

BACKGROUND AND OBJECTIVES: Many studies of laser-induced thermal decomposition of dental enamel have demonstrated a reduction in the rate of acid dissolution, size of artificial caries-like lesions, and acid reactivity. Additionally, studies have correlated the loss of carbonate from dental enamel with a reduction in acid dissolution. Dental mineral consists of hydroxyapatite with many substitutions, the major one being carbonate ( approximately 3-5% by weight), which markedly affects acid reactivity. The principle objective of the present work was to determine the precise depth of modification, i.e. , thermally induced decomposition of dental enamel (carbonate loss), at the predicted optimum laser irradiation parameters. STUDY DESIGN/ MATERIALS AND METHODS: Bovine enamel blocks were irradiated at lambda = 9.6 microm with 2-microsec and 100-microsec pulses and at lambda = 10.6 microm with 2-microsec pulses. Carbonate loss was calculated from infrared spectra as a function of depth and compared to numerical simulations of the maximum temperature rise. RESULTS: Carbonate loss was initiated at temperatures greater than 400 degrees C, but was complete only after repeated irradiation of the surface above the melting threshold. Carbonate loss of dental enamel irradiated at 9.6 microm with a 100-microsec pulse and at 10.6 microm with a 2-microsec pulse was greater than that of enamel irradiated at 9.6 microm with a 2-microsec pulse. The depth of carbonate loss in dental enamel irradiated with a 2-microsec pulse was greater for lambda = 10.6 microm than for lambda = 9.6 microm. CONCLUSION: The depth of modification is consistent with the presented model that incorporates the absorption depth and thermal relaxation time/pulse duration. However, repeated irradiation is required for complete removal of carbonate, depending on absorption depth and pulse duration.

Animals↗

PubMed1999

Prevention and reversal of dental caries: role of low level fluoride.

Dental caries is a bacterially based disease that progresses when acid produced by bacterial action on dietary fermentable carbohydrates diffuses into the tooth and dissolves the mineral, that is, demineralization. Pathological factors including acidogenic bacteria (mutans streptococci and lactobacilli), salivary dysfunction, and dietary carbohydrates are related to caries progression. Protective factors which include salivary calcium, phosphate and proteins, salivary flow, and fluoride in saliva can balance, prevent or reverse dental caries. Fluoride works primarily via topical mechanisms which include (1) inhibition of demineralization at the crystal surfaces inside the tooth, (2) enhancement of remineralization at the crystal surfaces (the resulting remineralized layer is very resistant to acid attack), and (3) inhibition of bacterial enzymes. Fluoride in drinking water and in fluoride-containing products reduces tooth decay via these mechanisms. Low but slightly elevated levels of fluoride in saliva and plaque provided from these sources help prevent and reverse caries by inhibiting demineralization and enhancing remineralization. The level of fluoride incorporated into dental mineral by systemic ingestion is insufficient to play a significant role in caries prevention. The effect of systemically ingested fluoride on caries is minimal. Fluoride "supplements" can be best used as a topical delivery system by sucking or chewing tablets or lozenges prior to ingestion.

Adolescent↗

PubMed1999

Cysteine protease inhibitory activity and levels of salivary cystatins in whole saliva of periodontally diseased patients.

The 3 human salivary cystatins S, SA and SN are multifunctional proteins that possess a cysteine protease inhibitory property, but their ability to act as such is very different (SN > SA >> S). One form, S, also appears to possess antibacterial properties towards the bacterium Porphyromonas gingivalis, often associated with periodontal diseases. In this study we measured the total cystatin inhibitory activity and the levels of each salivary cystatin in the whole saliva of 8 periodontally diseased patients and 2 groups of control subjects (n = 6 and n = 10). The total cystatin inhibitory activity and the total salivary cystatin concentration in the periodontally diseased patients were found to be lower than the controls (p < or = 0.005). The concentration of S was depleted to levels that would not allow it to be an effective antibacterial agent, and the concentration of SA, although depleted in some cases, was still present at sufficient levels to allow it to act as an effective physiological inhibitor of cathepsin L. The concentration of cystatin SN was also depleted in the periodontally diseased patients, but was still present in sufficient quantities to act as an effective physiological cysteine protease inhibitor of cathepsins H and L. In comparison, the concentration of all 3 salivary cystatins in the control subjects were sufficient to enable these proteins to be both effective physiological cysteine protease inhibitors and antibacterial agents.

Adult↗

PubMed1999

Artificial caries removal and inhibition of artificial secondary caries by pulsed CO2 laser irradiation.

PURPOSE: To investigate the inhibition of artifical secondary caries around restorations placed after removal of artificial caries by pulsed CO2 laser irradiation and by mechanical means. MATERIALS & METHODS: Beveled cavities were prepared mechanically on the facial surfaces of extracted human molars. Each cavity was subsequently exposed to an artificial caries (demineralizing) solution (pH 5.0) for 7 d to generate a demineralized zone approximately 100-200 microns thick on the cavity surface. The artificial carious/demineralized zones of the cavities were removed by a pulsed CO2 laser operating at a wavelength of 9.3 microns with pulse duration of 100 microseconds and an irradiation intensity of 5 J/cm2. Artificial control caries were removed mechanically with a carbide bur in a slow speed handpiece. The cavities were slightly undercut and restored with a resin-based composite without etching and bonding and the restored teeth were subjected to pH cycling solutions for 10 d as follows: Demineralization solution, pH 4.5 for 6 hrs, followed by remineralization solution, pH 7.0 for 18 hrs. Cycled teeth were sectioned through the restorations and the resulting lesions were analyzed in thin section using polarized light and Knoop microhardness. RESULTS: Mean microhardness delta Z values, indicating mineral loss were: 549 (SD 191) for control, and 140 (SD 127) N = 11. This difference is significant with t = 5.543 and P = 0.000 (Paired t-test). Caries penetration: Control side--231 microns (SD 71), Laser treated side: 123 microns (SD 79) N = 6. This difference is significant with t = 5.198 and P = 0.003 (Paired t-test). The results show that the laser treatment not only removed artificial caries, but also inhibited decalcification of the cavity wall in a subsequent artificial caries challenge by as much as 81% compared to control samples. No etching and bonding was used in this pilot study, which might have influenced the results. Future studies should address the inhibition effect of the laser treatment as compared to adhesive techniques, fluoride treatments and fluoride release restorative materials. CONCLUSION: Caries removal by a pulsed lambda = 9.3 microns CO2 laser produces a cavity surface morphology with marked resistance to artificial secondary caries as compared to mechanical removal.

Carbon Dioxide↗

PubMed1998

CO2 laser inhibitor of artificial caries-like lesion progression in dental enamel.

Several studies during the last 30 years have demonstrated the potential of laser pre-treatment of enamel or tooth roots to inhibit subsequent acid-induced dissolution or artificial caries-like challenge in the laboratory. The overall objective of ongoing studies in our laboratories is to determine, systematically, the optimum sets of parameters for carbon dioxide laser irradiation that will potentially effectively inhibit dental caries in enamel and tooth roots. The aim of the present study was to examine the roles of wavelength and fluence in the prevention of caries progression in vitro in enamel by means of a pH-cycling model. The hypothesis to be tested was that the highly absorbed 9.3- and 9.6-microm wavelengths would be efficiently converted to heat, creating a temperature sufficiently high to reduce the acid-reactivity of the mineral and inhibit caries-like lesion progression in dental enamel. One hundred and sixty caries-free tooth crowns were cleaned and varnished with acid-resistant varnish, leaving one exposed window of enamel. Twelve groups of 10 enamel samples were irradiated in their individual windows by one of the four wavelengths (9.3, 9.6, 10.3, or 10.6 microm) of a tunable CO2 laser. Energy per pulse was 25, 50, 100, 200, or 250 mJ (25 pulses). Repetition rate was 10 Hz, and beam diameter was 1.6 mm. Fluence conditions of 1 to 12.5 J/cm2 per pulse were produced. All teeth, including 40 non-irradiated controls, were subjected to pH-cycling to produce artificial caries-like lesions. Results were assessed by cross-sectional microhardness testing. Inhibition of caries progression of from 40% to 85% was achieved over the range of laser conditions tested. At 9.3 and 9.6 microm, 25 pulses at absorbed fluences of 1 to 3 J/cm2 produced inhibition on the order of 70% with minimal subsurface temperature elevation (< 1 degree C at 2 mm depth), comparable with inhibition produced in this model with daily fluoride dentifrice treatments. Safety and efficacy studies will be required in animals and humans before these promising laboratory results can be applied in clinical practice.

Absorption↗

PubMed1998

Caries prevention by CO2 laser treatment: dependency on the number of pulses used.

The aim of this study was to assess the caries-preventive potential of various carbon dioxide laser conditions and to explore the effect of the number of laser pulses used. The authors irradiated unerupted human molars at two wavelengths--10.6 or 9.6 micrometers--and at 1, 5, 25 or 100 pulses. All teeth were then subjected to pH cycling simulating the conditions for caries progression. Pulsed CO2 laser-preventive treatment inhibited caries-like lesion progression by up to 87 percent. This effect was dependent on the number of pulses used, but there was no correlation between caries resistance and enamel surface morphological changes.

Acetates↗

PubMed1997

Permanent and transient changes in the reflectance of CO2 laser-irradiated dental hard tissues at lambda = 9.3, 9.6, 10.3, and 10.6 microns and at fluences of 1-20 J/cm2.

BACKGROUND AND OBJECTIVE: Effective use of lasers for preventive dental treatments requires accurate knowledge of the amount and distribution of laser energy deposited during irradiation. At CO2 wavelengths, the reflection losses are considerable and reduce the laser energy absorbed by the tissue surface. STUDY DESIGN/MATERIALS AND METHODS: The specular and diffuse reflectance of enamel and dentin were measured at the 10.6-, 10.3-, 9.6-, and 9.3-microns wavelengths of the CO2 laser. Changes in reflectance during and after laser irradiation were investigated. RESULTS: The low-fluence reflectance (< 1 J/cm2) of calcified dental tissues at CO2 wavelengths varies between 9% and 50%. Permanent and transient changes in the reflectance are induced at higher irradiation intensities. CONCLUSION: These changes resulted in increased energy coupling during irradiation.

Animals↗

PubMed1997

Magnesium-containing carbonate apatites.

Hydroxyapatites precipitated at pH 7.0 and 9.0 with and without carbonate and with different amounts of magnesium were studied. Mg uptake, Ca/P ratios, and lattice constant data indicate that Mg is incorporated into the apatite lattice. IR spectra demonstrate the formation of B-type carbonate apatites with carbonate substituting for phosphate. Decomposition of carbonate-containing apatites at elevated temperatures up to 1000 degrees C is more gradual for apatites prepared at pH 9.0 than for those prepared at pH 7.0 for which an abrupt loss of carbonate occurs after 600 degrees C. Compounds synthesized without added carbonate partially transform to beta Ca3(PO4)2 (TCP) at about 700 degrees C. Greater transformation to TCP occurs as the Mg incorporation is increased, indicating the insertion of Mg into TCP and consequent stabilization of the TCP. SEM micrographs show increases in the size of crystallites when apatites are precipitated with Mg (in the 0.2-1.5% range), providing further evidence for Mg incorporation into the apatite structure.

Calcium↗

PubMed1997

Effects of collagenase on root demineralization.

The role of proteolytic enzymes in the root caries process remains unclear. The aim of this study was to investigate collagenase activity during tooth root demineralization and remineralization in an in vitro demineralization/remineralization pH-cycling model, Human tooth roots were subjected to pH cycling (alternating demineralization and remineralization) in one of two different time cycles for five days. Collagenase at 90, 180, or 360 micrograms per root was placed into either the demineralizing solution or the remineralizing solution in the pH-cycling system. The effects of additional exposure to collagenase before or after pH cycling were also studied. After the exposure, thin sections of the roots were examined histologically by polarized light microscopy. Changes of calcium and phosphate in the solutions were analyzed chemically. Surface erosion occurred only in the groups where collagenase was contained in the remineralizing solution and in which the root samples were exposed to severe demineralization. However, no differences among the control and experimental groups were found in calcium and phosphate changes in the pH-cycling solutions. These findings suggest that collagenase works during the remineralizing phase and predominantly attacks the organic matrix of the root after demineralization. Additional exposure to collagenase before or after pH cycling did not increase surface erosion except for exposure to collagenase in the absence of phosphate following pH cycling.

Calcium↗

PubMed1997

Effect of metabolic acidosis on the potassium content of bone.

Metabolic acidosis induces resorption of cultured bone, resulting in a net efflux of calcium (Ca) from the bone and an apparent loss of mineral potassium (K). However, in these organ cultures, there is diffusion of K between the medium and the crystal lattice, causing difficulty in interpretation of the acid-induced changes in mineral ion composition. To determine the effects of acidosis on bone mineral K, we injected 4-day-old neonatal mice with pure stable isotope 41K, equal to approximately 5% of their total body K. Calvariae were dissected 24 h later and then cultured for 24 h in medium without added 41K, either at pH approximately 7.4 (Ctl) or at pH approximately 7.1 (Ac), with or without the osteoclastic inhibitor calcitonin (3 x 10(-9) M, CT). The bone isotopic ion content was determined with a high-resolution scanning ion microprobe utilizing secondary ion mass spectrometry. 41K is present in nature at 6.7% of total K. The injected 41K raised the ratio of bone 41K/(39K+41K) to 9.8+/-0.5% on the surface (ratios of counts per second of detected secondary ions, mean+/-95% confidence interval) but did not alter the ratio in the interior (6.9+/-0.4%), indicating biological incorporation of the 41K into the mineral surface. The ratios of 41K/40Ca on the surface of Ctl calvariae was 14.4+/-1.2, indicating that bone mineral surface is rich in K compared with Ca. Compared with Ctl, Ac caused a marked increase in the net Ca efflux from bone that was blocked by CT. Ac also induced a marked fall in the ratio of 41K/40Ca on the surface of the calvariae (43+/-0.5, p < 0.01 vs. Ctl), which was partially blocked by CT (8.2+/-0.9, p < 0.01 vs. Ctl and vs. Ac), indicating that Ac causes a greater release of bone mineral K than Ca which is partially blocked by CT. Thus, bone mineral surface is rich in K relative to Ca, acidosis induces a greater release of surface mineral K than Ca, and osteoclastic function is necessary to support the enriched levels of surface mineral K in the presence of acidosis.

Acidosis↗